1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for processing multivalued image data in an area corresponding to an overlapped portion of nozzle arrays in order to record an image by using a recording head in which a plurality of nozzle arrays are arranged so that the overlapped portion is included in a direction crossing a direction in which the nozzle arrays are arranged.
2. Description of the Related Art
Conventionally, a recording apparatus is known which uses a recording head (a connected head) in which chips including a nozzle array in which a plurality of nozzles are arranged are arranged in a zigzag pattern. It is known that, as a recording apparatus that uses the connected head, there is a recording apparatus using serial method for performing recording by causing a recording head to scan in a direction crossing the arrangement direction of recording elements and conveying a recording sheet (recording medium) in the arrangement direction of the recording elements. It is also known that, as a recording apparatus that uses another recording method, there is a full-line type recording apparatus in which a recording head in which nozzles (discharge ports) are arranged in the entire recording width of the recording sheet is fixed and recording is performed by conveying the recording sheet in a direction crossing the arrangement direction of the recording elements. In particular, the full-line type recording apparatus uses a recording head in which nozzles (discharge ports) are arranged in the entire recording width of the recording sheet and continuously performs recording of an image of a recording width as the recording medium is conveyed, so that the full-line type recording apparatus can perform high-speed recording.
However, the connected head has a problem as described below. In the connected head, there is an overlapped portion where chips are overlapped with each other in a direction crossing the nozzle arrangement direction, and in the overlapped portion, registration between chips (relationship among relative recording positions of dots) may be out of alignment due to various reasons. Thus, density unevenness and granularity unevenness occur in the overlapped portion, and image quality decreases. The reasons why the registration between the chips gets out of alignment include a problem of accuracy of mounting of chips and a problem of accuracy of conveyance of a recording medium.
In Japanese Patent Laid-Open No. 5-57965, as a method for suppressing streaky image defect that occurs in the overlapped portion of the connected head, a method (hereinafter referred to as gradation mask) for complementarily increasing or decreasing recording duty in the overlapped portion of the chips by using a mask is disclosed.
As a technique for compensating the misalignment of the registration, Japanese Patent Laid-Open No. 2000-103088 discloses an image data processing method for increasing “robustness” against misalignment of registration (hereinafter also referred to as registration misalignment) between paths in multi-path recording. Here, the “robustness” means a resistance characteristic against density unevenness or the like caused by various errors. The above patent document focuses attention on a fact that fluctuations in image density caused by fluctuations in various recording conditions result from a fact that pieces of binary image data corresponding to different recording scans are in a complete mutual complementary relationship. The patent document recognizes that, when pieces of image data corresponding to different recording scans are generated so that the complementary relationship is reduced, multi-path recording having a good “robustness” can be realized”.
Therefore, in the technique disclosed in Japanese Patent Laid-Open No. 2000-103088, multivalued image data before binarization is divided into a plurality of planes, and these divided multivalued data are individually binarized. In this way, even when pieces of image data corresponding to different recording scans are misaligned with each other and recorded, large density fluctuations do not occur. A supplementary description of “plane” is given here. When original image data is divided corresponding to a plurality of recording scans and/or a plurality of nozzle arrays, the original image data is considered to be an overlap of the plurality of divided image data. Therefore, each divided image data is considered to be one “plane”. In the above-described Japanese Patent Laid-Open No. 2000-103088, one recording scan (path) corresponds to one plane.